The long-term goal is to compare Babesia microti transmission to Borrelia burgdorferi transmission. Such information will assist public health officials advising residents of endemic areas, attempting to minimize risk of infection with these two Ixodes dammini-borne pathogens. The specific aims are: 1) Evaluate the role of larval and adult I. dammini as vectors of Babesia and spirochetes. 2) Determine the duration of tick attachment required for pathogen transmission. 3) Identify the route(s) of spirochete transmission from I. dammini to vertebrate hosts. 4) Test the vector competence of tick species other than I. dammini for transmitting Babesia and spirochetes. 5) Describe the most efficient methods for detecting spirochetes in ticks and vertebrate hosts. Special emphasis will be placed on determining whether tick species affecting human populations in the southeastern United States are competent vectors of Ba. microti and Bo. burgdorferi. A basic understanding of the differences in the transmission dynamics of Ba. microti and Bo. burgdorferi that result in the disparate epidemiological patterns of human babesiosis and Lyme disease will be helpful in establishing global strategies for combating tick-borne disease.